Fixed #3232216: Unable to translate menu items

When a menu link entity was built on form submission, the icon value was not set on it as was set and saved later in the own form submit callback. This mismatch with the original entity caused the validation error. Using entity builder to set the icon value has fixed the issue.

Other than that translation settings are made to be respected: the icon value is shared between all translations, and the icon select is either hidden on translated menu item form when it's set to hide untranslatable fields.